Copper Flashings - A Manual - 1925 - Page 26
Figs. 67, 68, 69, 70, 71. These drawings are based on the standard details and practice of the Master Sheet Metal Roofers Association of Boston, Mass., and are reproduced by their permission. They show the methods used by this Association for flashing the copings as well as the front and rear faces of parapet walls as found on factories throughout New England. Where heavy snowfalls and sudden thaws are to be expected, and it is fundamental in the design of a factory that the temperature and humidity of the interior be kept nearly constant, the problem of flashing must be studied with great care. Ordinary flashing methods are insufficient, for they do not completely damp-proof the interior. It is necessary to devise means of cutting off any dampness or moisture which might seep down through the brick work during a driving rain or when the roof is covered with a foot or more of water-soaked snow.
These details represent the practical solution of this problem by those most familiar with the conditions to be overcome.
Fig. 67 shows a flashing for a brick wall less than 24 inches high. The base flashing is carried as a sheathing the full height of the wall and is covered by the cap flashing on the top of the wall. The sheets forming this sheathing are joined by soldered flat seams. (Compare with Fig. 70). The cap flashing, formed as shown to give it stiffness, extends over the top of the wall and is riveted on both sides to copper straps placed two feet apart. After the cap is set these straps are secured on the outside by nails driven into the joints of the brick work, and on the inside by soldering to the sheathing. The top of the wall should be sloped slightly to drain inward. The cap flashing is usually bedded in cement mortar. The base flashing is fastened to the rooting as described under "Base Flashings" below.
Fig. 68 shows a method of flashing under a coping. The cap flashing extends through the wall under the coping and turns down ½ inch on the outside and 3 inches on the inside. The exposed edge is turned back on itself ½ inch for stiffness. The coping is held in place by dowels which are made water tight with thimbles as described in Fig. 66.
Fig. 69. A fire-wall is flashed with copper as shown in Fig. 69. The cap flashing is similar to that shown in Fig. 67. It is bedded in cement mortar, extends down the wall on both sides 4 inches, and is fastened to the sheathings or base flashings by copper straps secured as described in Fig. 67. The top of the wall is sloped for drainage.
Fig. 70 shows a flashing for a brick wall more than 24 inches high. The cap flashing is used over a wood coping piece, and may be fastened in two ways. The lower figure uses the same method as is shown in Figs. 67 and 69, the cap flashing being held by brass wood screws. The alternate method illustrated at the top is better, as the overhang of the wood coping allows the screws to be placed underneath where water cannot enter the hole in the metal. This does away with soldering the screw heads. The cap flashing also has a drip on the outside which keeps the wash away from the brick work.
The base flashing is formed as standing seam sheathing. It is held at the top by the screws used to fasten the cap piece, and extends down to lap the cap flashing set in the brick work in the usual manner. (Figs. 48 and 49). The base flashing is placed as described under "Base Flashings" below. The advantage of this double flashing is in the extra safeguard provided against water finding its way back of the base flashing.
Fig. 71. A flashing for a Brick parapet wall faced with stone is shown here. The counter-flashing extends through the brick backing and into the joint of the stone courses one inch. This makes a cut-off against seepage. The base flashing is placed as described under "Base Flashings" below. Where this method is used with a wall exposed to heavy wind pressure the counter flashings should be keyed (as shown in Fig. 62).
BASE FLASHINGS FOR BUILT-UP ROOFING
Attention is directed to the U. S. Government Master Specifications for the Installation of Metal Flashings with Built-up Bituminous Roofing, adopted by the Federal Specifications Board on June 1, 1924, as Specification No. 156.
Where used against vertical walls this specification calls for three layers of felt saturated with pitch and extending 6 inches up the walls and out over the roofing felt to lap 6, 5, and 4 inches, respectively. A strip of metal is then rounded, not sharply bent, into the proper shape and set in the angle against the layers of felt. This strip of metal extends out on the roof at least 6 inches and up on the wall at least 5 inches.
When used with board sheathing the strip is nailed at the edge every six inches to the roof boards through the roofing. Over the metal strip on the roof two plies of felt at least 15 inches wide are laid. These are thoroughly cemented to each other and the roofing by hot pitch.
The association agrees with the recommendations of the Federal Specifications Board for base flashings.
The method of securing cap-flashings in reglets and brick work shown elsewhere in this book differs from that recommended by the Federal Specifications Board as the Association believes that it is better to build flashings into brick work than to place them in grooves made in the joints.
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